The present invention relates to a method of insulating a member, such as a cryogenic tank, pipe, or other cryogenic or extreme temperature member with multilayer insulation, and a packaged multilayer insulation blanket for use in the method.
Multilayer insulation has been used for quite some time to insulate cryogenic tanks, cryogenic pipes, and other cryogenic or extreme temperature containers, members or elements such as superconducting magnet assemblies or power distribution devices, etc. Multilayer insulation for the above purposes is described, for example, in U.S. Pat. No. 5,590,054 to McIntosh. This patent describes a variable density multilayer insulation formed of alternating layers of separator materials such as glass fiber materials, and heat radiation barriers such as metal foil, such as copper or aluminum foil, or double aluminized Mylar (DAM).
It has also been known, prior to the above McIntosh patent, that thermal radiation heat transfer, as defined by the Stephan-Boltzmann law, that heat transfer between parallel surfaces is a function of the emissivities of the surfaces and the warm absolute temperature taken to the fourth power against the cold absolute temperature taken to the fourth power. Because of the powerful effect of raising the temperatures to the fourth power, the impact of radiation between radiation barriers near a cold wall of a cryogenic vessel drops dramatically from the impact of radiation between radiation barriers near the vessel""s warm wall. Correspondingly, the temperature difference between the reflective barriers increases as the cold wall is approached. Thus, when cryogenic multilayer insulation is used to insulate between the inner and outer vessels of a Dewar vessel system, the heat reflective layers near the cold wall of the inner vessel are spaced further apart than the heat reflective layers closer to the warm wall. For this reason, prior methods of wrapping cryogenic containers using an orbital or wrapping method are not necessarily optimized for thermal performance, because these methods are unable to produce variable density multilayer insulation of the highest thermal efficiency.
Because the advantages of multilayer insulation have long been known, many methods have been proposed to simplify the installation of such multilayer insulation on large containers or tanks.
U.S. Pat. No. 4,104,783, to Schultz, et al., for example, discloses a method of installing multilayer insulation on the outside of a tank, by winding insulation and wire mesh around a cryogenic tank to form such a structure. A similar method is also disclosed in U.S. Pat. No. 3,241,702, to C. R. Navikas. By this latter method, alternating layers of glass fiber sheet material and perforated aluminum foil are wrapped around a cryogenic tank using a relatively complicated assembly of rollers, tensioners and apparatuses for holding and turning the containers or tank to be insulated. The multilayer insulation is wrapped around the container in a manner such that the ends of the insulation extend beyond the dimensions of the container and can be folded down and taped in place to insulate the entire container. An inner container thus wrapped is then inserted in an outer container to form a Dewar vessel construction.
More sophisticated methods of insulating cryogenic containers or vessels are disclosed in U.S. Pat. No. 4,741,456, to Faudou, et al., and U.S. Pat. No. 5,749,537, to Muzio, Jr., et al. The above Faudou., et al. patent discloses a method in which several insulating layers are helically wound around a tank which is supported and rotated about an axis by a shaft.
The Muzio, et al. patent discloses a number of prior art methods of wrapping cryogenic insulation around an inner tank of a Dewer vessel system in which alternating layers of cryogenic insulation paper and foil are wrapped around the tank in what is referred to as xe2x80x9cserial wraps.xe2x80x9d Each wrap consists of insulating paper spacer with metal foil centered thereon. An edge portion of the insulating paper abuts an edge portion of an adjacent layer or slightly overlaps the adjacent layer. While alternating layers of foil are slightly narrower in width than the insulated paper so that the edges do not contact one another. By this serial wrapping technique, it is ensured that alternating layers of insulating paper and foil are provided without significant xe2x80x9cheat shortsxe2x80x9d in which the cold side of one foil layer contacts the hot side of an adjacent foil layer. This method also requires considerably complicated and expensive machinery for holding the container to be insulated, for adjusting tension on the separately stored paper and foil layers and a frame suitable of supporting the entire apparatus. As can be appreciated by viewing the apparatus of Muzio, Jr., et al., a complicated and unwieldy drive means is provided including shafts, drives, translation devices, and tension devices, as well as a suitable braking system for providing adjustable tension control for the various rollers, and a frame for supporting the rollers, container, etc. Such large and complicated apparatuses are certainly not easily applicable to every situation in which a cryogenic container or other member needs to be wrapped with multilayer insulation. In addition, considerable skill and specialized training is required to operate the apparatus. Also, the Muzio, Jr. method, like other prior art methods can not easily be applied to thermally efficient, variable layer multilayer insulation.
It is therefore an object of the present invention to provide a method of insulating a cryogenic member such as a cryogenic container or tank, cryogenic pipe, or other cryogenic or extreme temperature member with multilayer insulation with a minimum of expense, in order to solve the problems of the prior art.
It is further object of the present invention to provide a method of insulating a cryogenic member such as a cryogenic container or tank, cryogenic pipe, or other cryogenic or extreme temperature member quickly, efficiently, and without the need for special equipment.
It is a particular object of the present invention to provide a method of insulating a cryogenic member such as a cryogenic container or tank, cryogenic pipe, or other cryogenic or extreme temperature member that is superior to the spiral or orbital wrapping technique conventionally used. The present invention strives for a method that avoids the labor- and time-intensive method of carefully rolling foil and spacer material onto the vessel without creating leaks or heat shorts.
It is a still further object of the invention to provide a method which can vary the thickness and/or quantity of spacer material between layers in any desired fashion.
It is also an object of the present invention to provide a packaged multilayer insulation and a method of packaging and producing fragile, multilayer insulation, particularly variable density multilayer insulation blankets or composites, which can be easily transported without damage and applied without special training and without significant time, labor, or complicated apparatuses.
It is also an object of the present invention to provide a method of packaging and a packaged insulation wherein the multilayer insulation is packaged and can be transported with low or no moisture content so that any subsequent evacuation required during the installation of the insulation is simplified.
In accordance with the present invention, and in order to solve the above and other objects, the present invention provides a method of insulating a member, such as a cryogenic tank, pipe, or other cryogenic or extreme temperature element with multilayer insulation, and a packaged multilayer insulation blanket for use in the method.
According to the present invention, a method is provided of insulating a member with multilayer insulation, comprising the following steps. First, a packaged multilayer insulation blanket is provided. The packaged blanket includes (1) a multilayer insulation blanket including a plurality of alternating layers of heat-reflective foil and insulation spacer material, and (2) two layers of plastic sheeting sandwiching the multilayer insulation blanket therebetween, each layer having at least one edge, wherein the edge of the plastic sheeting is sealed to thus define an inside space containing the multilayer insulation. The inside space is preferably evacuated, partially evacuated, purged of air with an inert gas, or otherwise kept dry or in a low moisture state. Second, the edge of the packaged insulation is opened and an edge of the multilayer insulation blanket is attached to the member to be insulated. Third, the multilayer insulation is guided onto or around the member, and out from between the plastic sheeting until edges of the multilayer insulation abut. Lastly, the abutting edges of the multilayer insulation blanket are attached with any appropriate means such as heat reflective tape, or other fasteners. Preferably, reflective tape is used to ensure that no leaks or xe2x80x9cheat shortsxe2x80x9d result after the insulation is applied. The member to be insulated by the method according to the present invention can be a cryogenic container, such as the inner container of a Dewar structure having an inner container, an outer container, and evacuated space therebetween. The member can also be a cryogenic pipe, a heat shield for a spacecraft, superconducting power distribution equipment, such as superconducting magnets, or any one of a number of cryogenic or extreme temperature applications.
The heat reflective foil of the multilayer insulation is preferably aluminum foil, but can be any other suitable material such as double aluminized Mylar (DAM). The insulation spacer material is preferably microfiberglass insulation.
The method, in a preferred embodiment, comprises the further steps of providing a second packaged multilayer insulation blanket and installing it around the first multilayer insulation blanket so that the abutting edges of the second multilayer insulation blanket are offset from the abutting edges of the first multilayer insulation blanket.
The invention also relates to a packaged multilayer insulation blanket comprising (1) a multilayer insulation blanket including a plurality of alternating layers of heat-reflective foil and insulation spacer material, and (2) two layers of plastic sheeting sandwiching the multilayer insulation blanket therebetween, each layer having at least one edge, wherein the edge of the plastic sheeting is sealed to thus define an evacuated inside space containing the multilayer insulation.
Further objects, features and advantages of the present invention will become apparent from the detailed description of the preferred embodiments, when considered together with the attached figures of drawing.